Bismaleimides chemistry

Bismaleimides - Bismaleimides resins were first introduced into the market in the early 1970 s. As with other resin systems, there are many variations of bismaleimides. The Kermid and Kinel bismaleimide products as marketed in the U. S. by Rhodia are representative examples. Bismaleimide chemistry is represented in Eq. 3 where curing can be accomplished thermally through the unsaturation in the maleimide or by way of the Michael Reaction where an appropriate curing agent such as aromatic diamine adds across the activated double bond. In most instances, a combination of curing thermally through the double bond and via an aromatic diamine is used in actual practice. Bismaleimides are frequently formulated... 

A number of BMI resias based on this chemistry became commercially available through Rhc ne Poulenc for appHcation ia priated circuit boards and mol ding compounds and Rhc ne Poulenc recognized the potential of bismaleimides as building blocks for temperature-resistant thermoset systems. The basic chemistry, however, was not new, because the Michael addition reaction had been employed by Du Pont to obtain elastomeric reaction products from bismaleimides and Hquid polymeric organic diamines (15). 

Propenylphenoxy compounds have attracted much research. BMI—propenylphenoxy copolymer properties can be tailored through modification of the backbone chemistry of the propenylphenoxy comonomer. Epoxy resins may react with propenylphenol (47,48) to provide functionalized epoxies that may be low or high molecular weight, Hquid or soHd, depending on the epoxy resin employed. Bis[3-(2-propenylphenoxy)phthalimides] have been synthesized from bis(3-rutrophthalimides) and o-propenylphenol sodium involving a nucleophilic nitro displacement reaction (49). They copolymerize with bismaleimide via Diels-Alder and provide temperature-resistant networks. 

A novel cure chemistry employed for addition poly(imides) has recently been published. The successful preparation of 4-aminobenzocyclobutene allowed the synthesis of benzocyclobutene-terminated imide oligomers and bisfbenzocylobutenes) (17). The benzocyclobutene group is a latent diene which isomerizes to o-guinodimethane at temperatures of about 200 °C and may homo- and/or co-polymerize for example with bismaleimide (83). Details on the benzocyclobutene chemistry are described in chapter I of this book. 

Winter H, Loontjens JA, Mostert Ham, Tholen MGW (1989) Chemistry and properties of new bismaleimides designed for improved processability. In Feger C, Khojasteh MM, McGrath JE (eds) Polyimides materials, chemistry and characterization. Elsevier, Amsterdam, p 229... 

A wide variety of polymers have been used including epoxies, bismaleimides and polyimides. One of the most common polyimides is PMR-15 [44]. The chemistry is complex, see Fig. 10.23, but consists essentially of two stages imidisation to give a norbomene end-capped... 

To the thermoset type belong bismaleimides and bisnadimides as well as oligomeric end capped imides. End capping occurs with reactive phen-ylethyl groups. These types are used for reactive injection molding and related techiuques. The chemistry of formation of the imide moiety is quite similar for both the thermoset type and the thermoplastic type. There are several monographs on PIs. Bismaleimides are a separate subclass... 

Pindur and Haber explored the chemistry shown in equation 2 and synthesized several new cycloadducts (Scheme 7, 6-12) from IQD 4 [52], The observed regiochemistry with unsymmetrical dienophiles (methyl acrylate, nitrosoben-zene, l,l-bis(phenylsulfonyl)ethane, methyl vinyl sulfone, and methyl vinyl ketone) was low to modest, with the major isomer as predicted by simple FMO theory. However, dienophiles acrolein, propynoates, and diethyl maleate were unreactive relative to dimerization of IQD 4. Pindur and Meyer prepared several bis(tetrahydropyrrolo[3,4- ] carbazoles) by exposing IQDs (generated as shown in equation 2) to alkane-tethered bismaleimides [53]. In two... 

Figure 2.35 Chemistry of the chain extension of bismaleimide resin...

Recently, CIBA-GEIGY introduced unique crosslinking chemistry into bismaleimide system by utilizing so-called... 

From the beginning one of the critical points in the chemistry of addition polyimides was to adjust the formulations in order to prevent brittleness of the final curing material. The first approach for improving the mechanical behaviour of poly(bismaleimides) was the incorporation of moieties which provide a separation of the two active maleimide groups. Diamines and dithiols have worked as very suitable spacers, capable to react with the double bonds of bismaleimides [301-304]. The reaction takes place by nucleophilic addition (Michael addition) on the electron-deficient double bond, which is activated by the two adjacent carbonyl groups (Scheme 56). The reaction is usually carried out in acidic solvents (m-cresol or DMF/acetic acid mixtures) to avoid cross-linking that occurs by reaction of the anionic intermediate with maleimide double bonds [305,306]. The mechanism for the reaction of thiols and maleimides is depicted in Scheme (56). 

The resin matrix is usually a formulated thermoset system (i.e. a reactive matrix, which on the application of heat and pressure, chemically reacts to form an infusible reinforced laminate). The thermosetting matrices are most often based on epoxy chemistries although there are plenty of examples of phenolic, bismaleimide and polyimide matrices (for example, the HexPly range from Hexcel Composites) and a few where the resin is based on cyanate esters. Thermoplastic matrices are also encountered (i.e. matrices that can change from a solidus to a liquidus form by tbe application of heat and pressure and then revert to the solid state on cooUng) which are usually, but not exclusively, based on polysulphone, polyetbersulphone or polyether ether ketone chemistries. 

With such a plethora of chemistries available, the adhesive formulator can generally tailor the adhesive to meet any required cure temperature — usually in the range of ambient (i.e. about 22°C) to as high as 230°C. Cure times can range from several seconds, particularly with polyurethane-based systems and to a certain extent with acrylic systems, to several hours, as is the case with bismaleimide and polyimide adhesives. In this latter instance, cure, or more usually post cure, temperatures as high as 300°C often have to be used to ensure that the final rearrangement reactions go to completion. 

A study was conducted to differentiate between the crosslinking reactions of bismaleimides and biscitraconimides in squalene as well as in NR. Bismaleimides were found to participate in the crosslinking reaction in the absence of curing compounds such as accelerators and sulphur. Biscitraconimides took part in the crosslinking reaction when polysulphidic crosslinks were under the process of degradation. Sulphur and accelerator were required for the formation of polysulphidic crosslinks and hence the presence of sulphur and accelerator were essential for biscitraconimide crosslinking. The differences in the reactivity and the chemistry of crosslinking are studied and discussed. Some application data are provided in order to elaborate on the differences. 17 refs. 

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